Pressure containers for storing gases tinder an internal pressure are traditionally made of metal, e.g., steel. To achieve adequate safety against failure and/or a permanent imperviousness, certain wall thicknesses must be maintained—depending on the choice of the metal material and the design of the pressure container. One disadvantage of all-metal pressure containers is relatively low storage efficiency (performance factor) based on weight.
A significant weight reduction with at least comparable functionality can be achieved if the pressure container is made not merely of metal but instead partially or entirely of a composite material. Such pressure containers must of course reliably meet the basic requirements, i.e., they must be impervious and must withstand operating stresses (e.g., the internal pressure). So-called type III pressure containers, as well as those of type II, have a metal liner, which essentially assumes the sealing function and to some extent also has a load-bearing function. To ensure adequate mechanical integrity, a composite fiber material (laminate) is used, e.g., made of epoxy resin-impregnated fiber strands (rowings [sic; rovings]) or tapes having a thermoplastic matrix, etc., that are used for complete winding in type III containers and for circumferential winding in type II. In most cases, carbon fibers are used as the fiber components. They have only one-quarter the density of steel but have approximately three times the static tensile strength of normal steel for seamless bottles. Carbon fibers also have a very low susceptibility to fatigue. Alternative options include aramid fibers, glass fibers and in the future there will also be new fibers (such as basalt fibers) or hybrid composites consisting of multiple fibers types. With these types of containers, the liner forms a type of basic structure and may be made of various materials, e.g., steel, aluminum or thermoplastic (type IV pressure container). The advantage of pressure containers made of composite materials lies primarily in the weight reduction, which may amount to up to 70% with comparable pressure containers made of steel with the same filling. Such pressure containers are used, for example, by emergency vehicles, fire departments and in medical areas. Other areas of use include storage devices for natural gas or hydrogen for use in aviation and space travel, hazardous goods shipping and automotive engineering.
Because of their hazard potential filling and shipping of pressure containers are subject to a general prohibition with reservation for issuance of a permit. A permit is issued only after relevant statutory provisions are met. In Europe, these prerequisites for approval include, for example, pressure testing by performing a leakage test on each individual container. No random sample pressure testing is allowed for the applications listed above. These also include various tests on random samples of each lot, including destructive tests.
The object of the present invention is to show a mesas by which the quality testing, acceptance testing or inspection testing of pressure containers made of composite materials can be performed easily and with a high reliability by using acoustic emission testing (AE testing). In particular, acoustic emission testing should be adapted to the needs of industrial manufacturing and inspection of pressure containers and should be compatible with existing manufacturing and inspection routines without any great effort. Furthermore, the method should be usable for optimizing container design and technical safety evaluation of the condition of a container during operation in the sense of heath/safety monitoring or recurring pressure testing.